Exhibit 10.3.1  SUPPLEMENTAL CONFIRMATION  To:
  
  Genzyme Corporation
  500 Kendall Street,
  Cambridge, MA 02142From:
  
  Goldman,
  Sachs & Co.Subject:
  
  Accelerated
  Stock BuybackRef.
  No:
  
  SDB
  1631 855 313Date:
  
  June 17,
  2010  
  The
purpose of this Supplemental Confirmation is to confirm the terms and
conditions of the Transaction entered into between Goldman, Sachs &
Co. (GS&Co.) and Genzyme Corporation (Counterparty)
(together, the Contracting Parties) on the Trade
Date specified below.  This Supplemental
Confirmation is a binding contract between GS&Co. and Counterparty as of
the relevant Trade Date for the Transaction referenced below.  1.             This Supplemental Confirmation
supplements, forms part of, and is subject to the Master Confirmation dated as
of June 17, 2010 (the Master Confirmation) between the Contracting Parties, as
amended and supplemented from time to time. 
All provisions contained in the Master Confirmation govern this
Supplemental Confirmation except as expressly modified below.  2.             The terms of the Transaction to
which this Supplemental Confirmation relates are as follows:  Trade
  Date:
  June 17, 2010Forward
  Price Adjustment Amount:
  USD [**]Calculation
  Period Start Date:
  June 18, 2010Scheduled
  Termination Date:
  October 18, 2010First
  Acceleration Date:
  [**]Prepayment
  Amount:
  USD1,000,000,000Prepayment
  Date:
  June 22, 2010  
 [**] = Portions of this exhibit have been
omitted pursuant to a confidential treatment request. An unredacted version of
this exhibit has been filed separately with the Commission.


Initial
  Shares:
  15,555,123 Shares; provided that if,
  in connection with the Transaction, GS&Co. is unable to borrow or
  otherwise acquire a number of Shares equal to the Initial Shares for delivery
  to Counterparty on the Initial Share Delivery Date, the Initial Shares
  delivered on the Initial Share Delivery Date shall be reduced to such number
  of Shares that GS&Co. is able to so borrow or otherwise acquire, and
  GS&Co. shall use reasonable good faith efforts to borrow or otherwise
  acquire a number of Shares equal to the shortfall in the Initial Share
  Delivery and to deliver such additional Shares as soon as reasonably
  practicable. The aggregate of all Shares delivered to Counterparty in respect
  of the Transaction to which this Supplemental Confirmation relates pursuant
  to this paragraph shall be the Initial Shares for the purposes of Number
  of Shares to be Delivered in the Master Confirmation.Initial
  Share Delivery Date:
  June 22, 2010Additional
  Relevant Days:
  The ten (10) Exchange Business Days
  immediately following the Calculation Period.Other:
  GS&Co. is paying a fee to another
  broker-dealer in connection with this Transaction.  Details are available upon request.  3.             Counterparty
represents and warrants toGS&Co.
that neither it nor any affiliated purchaser (as defined in Rule 10b-18
under the Exchange Act) has made any purchases of blocks pursuant to the
proviso in Rule 10b-18(b)(4) under the Exchange Act during either (i) the
four full calendar weeks immediately preceding the Trade Date or (ii) during
the calendar week in which the Trade Date occurs, except as otherwise disclosed
to GS&Co..  4.             This Supplemental Confirmation may
be executed in any number of counterparts, all of which shall constitute one
and the same instrument, and any party hereto may execute this Supplemental
Confirmation by signing and delivering one or more counterparts.  
 [**] = Portions of this exhibit have been omitted pursuant to a
confidential treatment request. An unredacted version of this exhibit has been
filed separately with the Commission.  2


Counterparty
hereby agrees (a) to check this Supplemental Confirmation carefully and
immediately upon receipt so that errors or discrepancies can be promptly
identified and rectified and (b) to confirm that the foregoing (in the
exact form provided by GS&Co.) correctly sets forth the terms of the
agreement between GS&Co. and Counterparty with respect to the Transaction
to which this Supplemental Confirmation relates, by manually signing this
Supplemental Confirmation or this page hereof as evidence of agreement to
such terms and providing the other information requested herein and immediately
returning an executed copy to Equity Derivatives Documentation Department,
facsimile No. 212-428-1980/83.  Yours
  sincerely,GOLDMAN,
  SACHS & CO.By:
  /s/
  Neasa DoyleAuthorized
  Signatory Vice PresidentName
  Neasa DoyleAgreed
  and Accepted By:GENZYME
  CORPORATIONBy:
  /s/
  Michael S. WyzgaName:
  Michael
  S. WyzgaTitle:
  Executive
  Vice President and Chief Financial Officer  
 [**]
= Portions of this exhibit have been omitted pursuant to a confidential
treatment request. An unredacted version of this exhibit has been filed
separately with the Commission.